Borosilicate optical crown glass with anomalous partial dispersions with negative deltave dispersion values



United States Patent Int. Cl. c03c3/04, 3/08 US. Cl. 106-54 4 Claims ABSTRACT OF THE DISCLOSURE Optical crown glasses with anomalous partial dispersion with negative Av values and improved chemical resistance properties, with mean refractive indices n from 1.54 to 1.58 and 1.61 to 1.64 can be produced from a mixture consisting essentially of 24 to 52 mol percent SiO 25 to 35 mol percent B 0 to 25 mol percent selected from the group consisting of oxides of alkali elements; 2 to 8 mol percent A1 0 up to 10 mol percent selected from the group consisting of oxides of the bivalent elements zinc, cadmium, and lead; 1 to 7 mol percent selected from the group consisting of oxides of tantalum and niobium; and optional additives up to mol percent selected from the group consisting of oxides of zirconium, lanthanum and tungsten.

METHODS OF PRODUCING SAID GLASSES Said glasses are combinable with glasses with equivalent positive Av values for apochromatic correction without influencing thereby other corrective conditions of an optical system.

CROSS-REFERENCES TO RELATED APPLICATIONS The present invention is a continuation-in-part of copending US. Pat. application Ser. No. 542,035 of the same co-inventors, filed Apr. 12, 1966, which issued as US. Pat. No. 3,451,829 and the priorities to which that patent is entitled are claimed for all subject matter common therewith.

BACKGROUND OF THE INVENTION Field of the invention Optical glasses with mean refractive index values 22 between 1.54 to 1.58 and 1.61 to 1.64, with dispersion values 1 of 45 to 60, and with negative Av values, their compositions, methods to produce them and their combination with glasses having positive Av values.

DESCRIPTION OF THE PRIOR ART Glasses with anomalous partial dispersion are known to the art. A basic differentiation is made as to whether these glasses, with respect to their partial dispersion, have higher or lower values than the normal glasses.

Normal glasses are defined as having a partial dispersion S'g which over a wide range is in approximately linear dependence from the mean dispersion value V Ordinarily, the aberration with respect to partial dispersion is indicated by the difference of the v value, with identical 2' value, between a normal glass and a glass with anomalous partial dispersion, and this difference is designated by Av Negative Av values are then equivalent to a lower partial dispersion, positive Av values are equivalent to a higher partial dispersion.

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Persons calculating the optical characteristics, namely the mean refractive index W and the Abbe number (relative dispersion) v i.e., for the refractive index values between :1.52 and n =l.64, and for the dispersion values of v 40 to 1 :60 must maintain certain limits with respect to the remaining important values. They seek to obtain, for glasses having positive Av values, glasses of the same optical position with negative Av values. A combination of two such glasses having different Av values makes possible a predetermined apochromatic correction, without influencing thereby other correction conditions of an optical system.

Glasses having positive Av values are described in applicants copending application Ser. No. 542,035, filed Apr. 12, 1966, now U.S. Pat. No. 3,451,829.

Glasses having negative Av values are described in U.S. Pat. No.\2,866 ,712. These glasses comprise as a vitrifying agent boric acid. Another type negative Av glass employs in addition thereto silicic acid. The proportions of boric acid generally are above 30% by weight and the additional proportion of silicic acid is up to 30% by weight. A further component in the known glasses are alkali oxides and lanthanum oxide, or zirconium oxide.

That applicants invention relates to an optical crown glass with anomalous partial dispersion having negative Av value and melted from a mix consisting by weight of the fusion of from 30% to 70% of boric acid anhydride, 2% to 30% of silica, 10% to 25% of zirconium oxide and over 10% of alkali metal oxide.

The inventors found that these glasses of the prior art have unsatisfactory chemical resistances, their compositions strongly tend to devitrify, and difficulties are encountered when melting them in commercially feasible batches.

SUMMARY OF THE INVENTION Thus the objects of the invention are: to avoid the shortcomings of the prior art glasses, mentioned above; to develop novel glasses, methods of producing them and compositions for making them; and to develop glasses of the type mentioned, which make it possible to combine them into combinations of two such. glasses having different Av values to permit a predetermined apochromatic correction, without adversely influencing other corrective conditions of an optical system.

Other objects and many of the attendant advantages of the present invention will become apparet to those skilled in the art from the following specification taken in conjunction with the various tables recited there-in, claims and drawing.

BRIEF DESCRIPTION OF THE DRAWINGS The only figure of the drawings is a flow chart of the method of producing optical crown glass with anomalous dispersion characterized by a -Av, 'value.

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the invention, the glasses are melted from mixtures comprising as essential ingredients:

24-52 mol percent SiO 2535 mol percent B 0 10-25 mol percent selected from the group consisting of oxides of the alkali elements,

2-8 mol percent A1 0 up to 10 mol percent selected from the group consisting of oxides of the bivalent elements zinc, cadmium and lead,

Sept. 22, 1979 BROMER ETAL 3,529fi8fi BOROSILICATE OPTICAL CROWN GLASS WITHANOMALOUS PARTIAL? DISPERSIONS WITH NEGATIVE a w DISPERSION vALuEs Filed April 28, 1967 FLOW CHART of the method of producing optical crown glass with anomalous dispersion A v value 1.) PREPARING A MIXTURE OF essential ingredients 2 l-52 mol S102 25-35 mol 9% B lo mol 96 selected from the group consisting of oxides of alkali elements 2-8 mol A- up to 10 mol U selected from the group consisting of oxides of the bivalent elements zinc, cadmium 80 lead l-T mol 1; selected from the group consisting of oxides of tantalum and niobium optional additives selected from the group consisting of oxides of zirconium, lanthanum 8c tungsten up to a total proportion of 15 mol 76 3.) EATING between oc & oc

5.) EIEVATING THE MPERATURE to about between 135090 to 1 120 0 6.) REFINING THE MELT under constant stirring for about to 200 minutes I a 7.) LOWERING THE TEMPERATURE under stirring to between 1100 0 and 1200 0 8.) FURTHER LOWERING THE TEMPERATURE without stirring to between 850C and 115oc 9.) CASTING THE GLASS INVENTORS:

at the later temperature HEINZ BROEMER and I NORBERT MEINERT ATTORNEY TABLE 2.EXAMPLES FOR GLASSES OF MEAN REFRACTIVE INDIOES as of from 1.54 to 1.58, with dispersion values w of 55 to 60 M01 Percent ZrOz Alla

Ila

M6112 N0. S103 B203 L120 Na20 Z110 A1205 4509807631099 L2 LL2 LL1LLO L 00333334308133 Q0 0 0 0 0 LL93 4 3 0 4263345155444. n2 &2 2 4-5 2 55553 8913329087674. Z7 4 4 &52 55 5 54- 1111111211111 5012212298884 16 1 3 3 0 $9999 94 223333m222223 6801069552227 2 4-L00 99 &9990w7 4444433333333 Weight Percent ZnO A1203 ZrOz T8205 Ave 6 5 55 5 5 5 5 5w55 m55555555555M 0000000000000 LLLZKLLLLLLZQ 0000000050500 11 LRwLL 7 6 11H1111 W 0000000000000 ml mlzizmlzmiiinm 0001100000001 6&6 6Xm&7 7 7 7 7 6 0000000000000 111:6 LLLLLLLAm 9.233%33333333 055 4 5 .a5 .a.a5 5 2 4433M33333333 TABLE 3.-EXAMPLES FOR GLASSES OF MEAN REFRACTIVE INDICES m of from 1.61 to 1.64, with dispersion values 0.. of to M01 Percent S102 B20 L120 NazO ZnO PbO A120 ZIOz TaZO Ava W0 Nb205 Melt No.

210989429 &&&2 224 960520507 5 3 4 0 2 w2nm222 2 132776866 0 7 8 &7 7 A3% 9 .22222 115508065 9&4 ada 4 2 2 3 Weight Percent S102 B20 L120 NazO ZnO PbO A1203 ZrOz T11201 Ave fimemnmem 9 7 6 5 4444M4444 ispermix- 55 minium phosphates from 45 to 55 percent, and alkaline earth phosphates from 5 to 10 percent as glass formers and optionally including additives selected from the group consisting by weight of alkali oxides from 10 to 20 percent, oxides of Mg, Ca, Sr, Ba, Zn, Cd from 15 to 30 percent and up to 10 percent of TiO We claim:

1. Optical crown glass with anomalous partial d sion characterized by a -Av value. melted from a ture consisting essentially of wag rm ATmOha e p a e g h .w0 i t .n 0 o S S mm .am. e Win md 6 mm m m copending patent application Ser. No. ,035, an optical crown glass with anomalous partial oxides of alkali elements, 2-8 mol percent A1 0 :1 0 g .m t. .B m 0 C p w r g m m fl d m onw .1 6 SB S CMW I I e P p p mmm mmm 255 3 L-S 0 2 21 in: ef Up to 10 mol percent selected from the group consisting of oxides of the bivalent elements zinc, cadmium and lead, 1-7 mol percent selected from the gro has been disclosed, having a positive deviation n, +Av up consisting of It is melted from a mix which consists by weight of aluoxides of tantalum and niobium.

3,529,980 7 8 2. Optical crown glass, with anomalous partial dis- 4. Optical crown glass as claimed in claim 1, said persion characterized by a -Av value, melted from a mixture consisting of mixture consisting essentially of:... s.

24-52 mol percent SiO Composition of mixture Mol percent Weight percent 25-35 mol percent B I g8} 3%: -25 mol percent selected from the group consisting of 18:7 628 oxides of alkali elements, 28 mol percent A1 0 3Z1 3: 1 Up to mol percent selected from the group consisting g3 of oxides of the bivalent elements zinc, cadmium and 2:3 3:4 lead, 3.9 20.8 1-7 mol percent selected from the group consisting of oxides of tantalum and niobium; and References Cited Up to 15 mol percent selected from the group consisting 1 UNITED STATES A S of oxides of zirconium, lanthanum and tungsten. 5 3. Optical crown glass as claimed in claim 1, said rnix- 2576521 11/1951 Kreldl et a1 106*54 tum Consisting of 2,745,757 5/1956 Geifcken 10654 2,866,712 12/1958 We1ssenberg et a1. 10647 3,143,432 8/1964 Bromer et a1. 106-54 Composition of mixture M01 percent Weight percent 3,174,871 3/1965 Geficken et a1 106 54 FOREIGN PATENTS g-g 863,352 3/1961 Great Britain.

2 2 88 HELEN M. MCCARTHY, Primary Examiner gig 13333 W. R. SATTERFIELD, Assistant Examiner 1. 0.25 US. Cl. X.R. 

